NEW YORK -- Yankees third baseman Aaron Boone injured his left knee playing basketball and might miss the season.

Boone was hurt Jan. 16 and may have torn his anterior cruciate ligament. He was examined three days later by Anaheim Angels team physician Dr. Lewis Yocum, and Boone informed the Yankees of the injury that night.

The extent of the injury will not be known until swelling subsides, and he has not yet been examined by Yankees' doctors.

Boone agreed Dec. 1 to a $5.75 million, one-year contract, and the contract contained language saying it would become nonguaranteed if he played basketball.

"Concerning his contract, I can confirm that there are certain prohibited activities, which include basketball," Cashman said.

If there is a complete tear, he would require reconstructive surgery that could keep him until 2005.

"We are currently evaluating the extent of the injury and expect to solicit multiple opinions before providing a complete diagnosis," general manager Brian Cashman said Monday.

The Yankees do not have a backup third baseman with full-time experience. Enrique Wilson and newly signed Miguel Cairo are options to fill the spot.

New York acquired Boone, who will turn 31 in March, from Cincinnati on July 31, and his 11th-inning homer off Boston's Tim Wakefield in Game 7 of the AL Championship Series won the pennant for the Yankees.

Boone is eligible for free agency after next season, and if the Yankees successfully converted the deal to a nonguaranteed contract, they could release him and be responsible for only 30 days' termination pay, about $942,000.

Minor leaguer Drew Henson was hoped to be an option at third this season, but he's struggled mightily in the Yankees' farm system and the trade for Boone signaled that New York did not think Henson would be ready for 2004.

The Yankees and Henson's representatives recently have had talks toward severing his ties with the team.

Henson, the former University of Michigan quarterback, agreed to a $17 million, six-year contract with the Yankees in 2001. He hit .234 with 14 homers, 40 doubles and 78 RBI at Triple-A Columbus this season. But he also struck out 122 times and made 28 errors at third.